I'm running 12.07 on an acer aspire and have had no problems, until I disabled the touchpad using the Fn and F7 keys. This disabled the touchpad fine. But when I went to turn it back on I got the enabled icon appear but the pad didn't work. The computer has been rebooted since this happened but this has made no difference. It is enabled in the settings, usb mouse works fine.
I have the same issue in my aspire 5738zg. I tried all the ubuntu since 9.04 with no luck, and some other distros as well. After reading almost every forum i could find, i came to the conclusion that the system fails to load the module after it's disabled. You could try to unload/load the modules directly:
This should make your touchpad work again...